Polycyano norbornenes are amorphous thermoplastics that have a glass transition temperature of about 135.degree. C., outstanding oil resistance due to the high nitrile content, and a high heat distortion temperature of about 110.degree. C. They have other desirable properties, such as resistance to hydrocarbon solvents (including aromatics), an excellent barrier to carbon dioxide and oxygen, good tensile strength, and they process easily on roll mills and in injection molding machines.
The main drawbacks of these polymers are their low impact strength which is less than about 0.5 J/cm. Unlike the polyalkyl norbornenes, which can have their impact strength enhanced by the addition of calcium stearate or ethylene-vinylacetate copolymer, it was not possible to improve impact strength of polycyano norbornenes in such a manner. This is surprising in view of the structural similarity of polyalkyl norbornenes and polycyano norbornenes and in view of the fact that the two polymer classes can be prepared by the ring-opening polymerization technique.
It is, therefore, desirable to retain the beneficial properties of the polycyano norbornenes and to improve impact strength thereof.